1. Field of the Invention
The present invention relates to a channelizer for RF signals and more particularly to an optical RF channelizer, for example, for use for RF spectral analysis, for optically channelizing RF signals modulated onto an optical carrier by optically separating the RF spectrum.
2. Description of the Prior Art
Communications systems, and in particular, military communications systems, are increasingly being driven toward higher frequencies and larger bandwidths by user requirements. For example, available communication bandwidth is disappearing as the number of users and the bandwidth per user escalates, forcing communication links to ever higher frequencies. In addition, modern missile seekers and imaging radar systems are utilizing frequencies as high as 94 GHz to achieve antenna directivity and higher resolution for small aperture systems. In order to accommodate relatively high bandwidth and high frequencies, RF communications systems are known to employ optical carrier transmission of the RF signal. Examples of such systems are disclosed in U.S. Pat. Nos. 4,468,766; 4,695,790; 5,005,946; 5,347,535; 5,377,035; and U.S. statutory invention registration H1059.
Optical channelizers are used to perform spectral analysis of the newer high frequency communication signals. Such optical channelizers are known to process relatively wider bandwidths than comparable RF channelizers for real time identification of complex signals. Examples of such optical channelizers are disclosed in U.S. Pat. Nos. 4,460,250 and 4,695,795 and U.S. Statutory Invention Registration H1059. Such channelizers are used to channelize or divide up a relatively wide bandwidth signal into several sub-bands or channels. Such optical channelizers are known to process relatively wider bandwidths than known RF channelizers. However, many of the optical channelizers utilize acousto-optic technology and thus are limited to RF bandwidths of a few GHz. Examples of optical communication systems utilizing acousto-optic technology are disclosed in U.S. Pat. Nos. 4,448,494; 4,644,267; 5,005,946; 5,105,380; 5,327,142; and 5,363,221.
In other known communications systems, the channelizing is done in the RF band. In such systems, the RF signal is demodulated from the optical carrier and greatly amplified in order to achieve channelization.